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Auto merge of #23938 - nikomatsakis:invariant, r=pnkfelix
There are still some remnants we could remove from the compiler (e.g. references to "subtraitrefs"; traits still have variance entries in the variance table), but this removes all user-visible bits I believe. r? @pnkfelix Fixes #22806 (since such traits would no longer exist)
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‎src/libarena/lib.rs

+4-1
Original file line numberDiff line numberDiff line change
@@ -192,13 +192,16 @@ struct TyDesc {
192192
align: usize
193193
}
194194

195+
trait AllTypes { fn dummy(&self) { } }
196+
impl<T:?Sized> AllTypes for T { }
197+
195198
unsafe fn get_tydesc<T>() -> *const TyDesc {
196199
use std::raw::TraitObject;
197200

198201
let ptr = &*(1 as *const T);
199202

200203
// Can use any trait that is implemented for all types.
201-
let obj = mem::transmute::<&marker::MarkerTrait, TraitObject>(ptr);
204+
let obj = mem::transmute::<&AllTypes, TraitObject>(ptr);
202205
obj.vtable as *const TyDesc
203206
}
204207

‎src/libcore/marker.rs

+34-73
Original file line numberDiff line numberDiff line change
@@ -35,6 +35,7 @@ use hash::Hasher;
3535
#[stable(feature = "rust1", since = "1.0.0")]
3636
#[lang="send"]
3737
#[rustc_on_unimplemented = "`{Self}` cannot be sent between threads safely"]
38+
#[allow(deprecated)]
3839
pub unsafe trait Send : MarkerTrait {
3940
// empty.
4041
}
@@ -50,6 +51,7 @@ impl !Send for Managed { }
5051
#[lang="sized"]
5152
#[rustc_on_unimplemented = "`{Self}` does not have a constant size known at compile-time"]
5253
#[fundamental] // for Default, for example, which requires that `[T]: !Default` be evaluatable
54+
#[allow(deprecated)]
5355
pub trait Sized : MarkerTrait {
5456
// Empty.
5557
}
@@ -203,6 +205,7 @@ pub trait Copy : Clone {
203205
#[stable(feature = "rust1", since = "1.0.0")]
204206
#[lang="sync"]
205207
#[rustc_on_unimplemented = "`{Self}` cannot be shared between threads safely"]
208+
#[allow(deprecated)]
206209
pub unsafe trait Sync : MarkerTrait {
207210
// Empty
208211
}
@@ -269,84 +272,41 @@ macro_rules! impls{
269272
)
270273
}
271274

272-
/// `MarkerTrait` is intended to be used as the supertrait for traits
273-
/// that don't have any methods but instead serve just to designate
274-
/// categories of types. An example would be the `Send` trait, which
275-
/// indicates types that are sendable: `Send` does not itself offer
276-
/// any methods, but instead is used to gate access to data.
277-
///
278-
/// FIXME. Better documentation needed here!
279-
#[stable(feature = "rust1", since = "1.0.0")]
275+
/// `MarkerTrait` is deprecated and no longer needed.
276+
#[unstable(feature = "core", reason = "deprecated")]
277+
#[deprecated(since = "1.0.0", reason = "No longer needed")]
278+
#[allow(deprecated)]
279+
#[cfg(stage0)]
280280
pub trait MarkerTrait : PhantomFn<Self,Self> { }
281-
// ~~~~~ <-- FIXME(#22806)?
282-
//
283-
// Marker trait has been made invariant so as to avoid inf recursion,
284-
// but we should ideally solve the underlying problem. That's a bit
285-
// complicated.
286281

282+
/// `MarkerTrait` is deprecated and no longer needed.
283+
#[unstable(feature = "core", reason = "deprecated")]
284+
#[deprecated(since = "1.0.0", reason = "No longer needed")]
285+
#[allow(deprecated)]
286+
#[cfg(not(stage0))]
287+
pub trait MarkerTrait { }
288+
289+
#[allow(deprecated)]
287290
impl<T:?Sized> MarkerTrait for T { }
288291

289-
/// `PhantomFn` is a marker trait for use with traits that contain
290-
/// type or lifetime parameters that do not appear in any of their
291-
/// methods. In that case, you can either remove those parameters, or
292-
/// add a `PhantomFn` supertrait that reflects the signature of
293-
/// methods that compiler should "pretend" exists. This most commonly
294-
/// occurs for traits with no methods: in that particular case, you
295-
/// can extend `MarkerTrait`, which is equivalent to
296-
/// `PhantomFn<Self>`.
297-
///
298-
/// # Examples
299-
///
300-
/// As an example, consider a trait with no methods like `Even`, meant
301-
/// to represent types that are "even":
302-
///
303-
/// ```rust,ignore
304-
/// trait Even { }
305-
/// ```
306-
///
307-
/// In this case, because the implicit parameter `Self` is unused, the
308-
/// compiler will issue an error. The only purpose of this trait is to
309-
/// categorize types (and hence instances of those types) as "even" or
310-
/// not, so if we *were* going to have a method, it might look like:
311-
///
312-
/// ```rust,ignore
313-
/// trait Even {
314-
/// fn is_even(self) -> bool { true }
315-
/// }
316-
/// ```
317-
///
318-
/// Therefore, we can model a method like this as follows:
319-
///
320-
/// ```
321-
/// use std::marker::PhantomFn;
322-
/// trait Even : PhantomFn<Self> { }
323-
/// ```
324-
///
325-
/// Another equivalent, but clearer, option would be to use
326-
/// `MarkerTrait`:
327-
///
328-
/// ```
329-
/// # #![feature(core)]
330-
/// use std::marker::MarkerTrait;
331-
/// trait Even : MarkerTrait { }
332-
/// ```
333-
///
334-
/// # Parameters
335-
///
336-
/// - `A` represents the type of the method's argument. You can use a
337-
/// tuple to represent "multiple" arguments. Any types appearing here
338-
/// will be considered "contravariant".
339-
/// - `R`, if supplied, represents the method's return type. This defaults
340-
/// to `()` as it is rarely needed.
341-
///
342-
/// # Additional reading
343-
///
344-
/// More details and background can be found in [RFC 738][738].
345-
///
346-
/// [738]: https://github.com/rust-lang/rfcs/blob/master/text/0738-variance.md
292+
/// `PhantomFn` is a deprecated marker trait that is no longer needed.
347293
#[lang="phantom_fn"]
348-
#[stable(feature = "rust1", since = "1.0.0")]
349-
pub trait PhantomFn<A:?Sized,R:?Sized=()> { }
294+
#[unstable(feature = "core", reason = "deprecated")]
295+
#[deprecated(since = "1.0.0", reason = "No longer needed")]
296+
#[cfg(stage0)]
297+
pub trait PhantomFn<A:?Sized,R:?Sized=()> {
298+
}
299+
300+
/// `PhantomFn` is a deprecated marker trait that is no longer needed.
301+
#[unstable(feature = "core", reason = "deprecated")]
302+
#[deprecated(since = "1.0.0", reason = "No longer needed")]
303+
#[cfg(not(stage0))]
304+
pub trait PhantomFn<A:?Sized,R:?Sized=()> {
305+
}
306+
307+
#[allow(deprecated)]
308+
#[cfg(not(stage0))]
309+
impl<A:?Sized,R:?Sized,T:?Sized> PhantomFn<A,R> for T { }
350310

351311
/// `PhantomData<T>` allows you to describe that a type acts as if it stores a value of type `T`,
352312
/// even though it does not. This allows you to inform the compiler about certain safety properties
@@ -444,6 +404,7 @@ mod impls {
444404
/// [1]: http://en.wikipedia.org/wiki/Parametricity
445405
#[rustc_reflect_like]
446406
#[unstable(feature = "core", reason = "requires RFC and more experience")]
407+
#[allow(deprecated)]
447408
pub trait Reflect : MarkerTrait {
448409
}
449410

‎src/libcore/nonzero.rs

+1
Original file line numberDiff line numberDiff line change
@@ -14,6 +14,7 @@ use marker::{Sized, MarkerTrait};
1414
use ops::Deref;
1515

1616
/// Unsafe trait to indicate what types are usable with the NonZero struct
17+
#[allow(deprecated)]
1718
pub unsafe trait Zeroable : MarkerTrait {}
1819

1920
unsafe impl<T:?Sized> Zeroable for *const T {}

‎src/librustc/middle/lang_items.rs

-1
Original file line numberDiff line numberDiff line change
@@ -321,7 +321,6 @@ lets_do_this! {
321321
ExchangeHeapLangItem, "exchange_heap", exchange_heap;
322322
OwnedBoxLangItem, "owned_box", owned_box;
323323

324-
PhantomFnItem, "phantom_fn", phantom_fn;
325324
PhantomDataItem, "phantom_data", phantom_data;
326325

327326
// Deprecated:

‎src/librustc/middle/traits/object_safety.rs

+4-5
Original file line numberDiff line numberDiff line change
@@ -138,11 +138,10 @@ fn supertraits_reference_self<'tcx>(tcx: &ty::ctxt<'tcx>,
138138
match predicate {
139139
ty::Predicate::Trait(ref data) => {
140140
// In the case of a trait predicate, we can skip the "self" type.
141-
Some(data.def_id()) != tcx.lang_items.phantom_fn() &&
142-
data.0.trait_ref.substs.types.get_slice(TypeSpace)
143-
.iter()
144-
.cloned()
145-
.any(is_self)
141+
data.0.trait_ref.substs.types.get_slice(TypeSpace)
142+
.iter()
143+
.cloned()
144+
.any(is_self)
146145
}
147146
ty::Predicate::Projection(..) |
148147
ty::Predicate::TypeOutlives(..) |

‎src/librustc/middle/traits/select.rs

-8
Original file line numberDiff line numberDiff line change
@@ -836,14 +836,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
836836
ambiguous: false
837837
};
838838

839-
// Check for the `PhantomFn` trait. This is really just a
840-
// special annotation that is *always* considered to match, no
841-
// matter what the type parameters are etc.
842-
if self.tcx().lang_items.phantom_fn() == Some(obligation.predicate.def_id()) {
843-
candidates.vec.push(PhantomFnCandidate);
844-
return Ok(candidates);
845-
}
846-
847839
// Other bounds. Consider both in-scope bounds from fn decl
848840
// and applicable impls. There is a certain set of precedence rules here.
849841

‎src/librustc/middle/ty_relate/mod.rs

+18-18
Original file line numberDiff line numberDiff line change
@@ -122,11 +122,11 @@ fn relate_item_substs<'a,'tcx:'a,R>(relation: &mut R,
122122
relate_substs(relation, opt_variances, a_subst, b_subst)
123123
}
124124

125-
fn relate_substs<'a,'tcx,R>(relation: &mut R,
126-
variances: Option<&ty::ItemVariances>,
127-
a_subst: &Substs<'tcx>,
128-
b_subst: &Substs<'tcx>)
129-
-> RelateResult<'tcx, Substs<'tcx>>
125+
fn relate_substs<'a,'tcx:'a,R>(relation: &mut R,
126+
variances: Option<&ty::ItemVariances>,
127+
a_subst: &Substs<'tcx>,
128+
b_subst: &Substs<'tcx>)
129+
-> RelateResult<'tcx, Substs<'tcx>>
130130
where R: TypeRelation<'a,'tcx>
131131
{
132132
let mut substs = Substs::empty();
@@ -161,11 +161,11 @@ fn relate_substs<'a,'tcx,R>(relation: &mut R,
161161
Ok(substs)
162162
}
163163

164-
fn relate_type_params<'a,'tcx,R>(relation: &mut R,
165-
variances: Option<&[ty::Variance]>,
166-
a_tys: &[Ty<'tcx>],
167-
b_tys: &[Ty<'tcx>])
168-
-> RelateResult<'tcx, Vec<Ty<'tcx>>>
164+
fn relate_type_params<'a,'tcx:'a,R>(relation: &mut R,
165+
variances: Option<&[ty::Variance]>,
166+
a_tys: &[Ty<'tcx>],
167+
b_tys: &[Ty<'tcx>])
168+
-> RelateResult<'tcx, Vec<Ty<'tcx>>>
169169
where R: TypeRelation<'a,'tcx>
170170
{
171171
if a_tys.len() != b_tys.len() {
@@ -264,10 +264,10 @@ impl<'a,'tcx:'a> Relate<'a,'tcx> for ty::FnSig<'tcx> {
264264
}
265265
}
266266

267-
fn relate_arg_vecs<'a,'tcx,R>(relation: &mut R,
268-
a_args: &[Ty<'tcx>],
269-
b_args: &[Ty<'tcx>])
270-
-> RelateResult<'tcx, Vec<Ty<'tcx>>>
267+
fn relate_arg_vecs<'a,'tcx:'a,R>(relation: &mut R,
268+
a_args: &[Ty<'tcx>],
269+
b_args: &[Ty<'tcx>])
270+
-> RelateResult<'tcx, Vec<Ty<'tcx>>>
271271
where R: TypeRelation<'a,'tcx>
272272
{
273273
if a_args.len() != b_args.len() {
@@ -629,10 +629,10 @@ impl<'a,'tcx:'a,T> Relate<'a,'tcx> for Box<T>
629629
///////////////////////////////////////////////////////////////////////////
630630
// Error handling
631631

632-
pub fn expected_found<'a,'tcx,R,T>(relation: &mut R,
633-
a: &T,
634-
b: &T)
635-
-> ty::expected_found<T>
632+
pub fn expected_found<'a,'tcx:'a,R,T>(relation: &mut R,
633+
a: &T,
634+
b: &T)
635+
-> ty::expected_found<T>
636636
where R: TypeRelation<'a,'tcx>, T: Clone
637637
{
638638
expected_found_bool(relation.a_is_expected(), a, b)

‎src/librustc_typeck/check/wf.rs

+7-35
Original file line numberDiff line numberDiff line change
@@ -117,15 +117,10 @@ impl<'ccx, 'tcx> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
117117

118118
self.check_variances_for_type_defn(item, ast_generics);
119119
}
120-
ast::ItemTrait(_, ref ast_generics, _, ref items) => {
120+
ast::ItemTrait(_, _, _, ref items) => {
121121
let trait_predicates =
122122
ty::lookup_predicates(ccx.tcx, local_def(item.id));
123-
reject_non_type_param_bounds(
124-
ccx.tcx,
125-
item.span,
126-
&trait_predicates);
127-
self.check_variances(item, ast_generics, &trait_predicates,
128-
self.tcx().lang_items.phantom_fn());
123+
reject_non_type_param_bounds(ccx.tcx, item.span, &trait_predicates);
129124
if ty::trait_has_default_impl(ccx.tcx, local_def(item.id)) {
130125
if !items.is_empty() {
131126
ccx.tcx.sess.span_err(
@@ -287,30 +282,7 @@ impl<'ccx, 'tcx> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
287282
ast_generics: &ast::Generics)
288283
{
289284
let item_def_id = local_def(item.id);
290-
let predicates = ty::lookup_predicates(self.tcx(), item_def_id);
291-
self.check_variances(item,
292-
ast_generics,
293-
&predicates,
294-
self.tcx().lang_items.phantom_data());
295-
}
296-
297-
fn check_variances(&self,
298-
item: &ast::Item,
299-
ast_generics: &ast::Generics,
300-
ty_predicates: &ty::GenericPredicates<'tcx>,
301-
suggested_marker_id: Option<ast::DefId>)
302-
{
303-
let variance_lang_items = &[
304-
self.tcx().lang_items.phantom_fn(),
305-
self.tcx().lang_items.phantom_data(),
306-
];
307-
308-
let item_def_id = local_def(item.id);
309-
let is_lang_item = variance_lang_items.iter().any(|n| *n == Some(item_def_id));
310-
if is_lang_item {
311-
return;
312-
}
313-
285+
let ty_predicates = ty::lookup_predicates(self.tcx(), item_def_id);
314286
let variances = ty::item_variances(self.tcx(), item_def_id);
315287

316288
let mut constrained_parameters: HashSet<_> =
@@ -331,7 +303,7 @@ impl<'ccx, 'tcx> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
331303
continue;
332304
}
333305
let span = self.ty_param_span(ast_generics, item, space, index);
334-
self.report_bivariance(span, param_ty.name, suggested_marker_id);
306+
self.report_bivariance(span, param_ty.name);
335307
}
336308

337309
for (space, index, &variance) in variances.regions.iter_enumerated() {
@@ -342,7 +314,7 @@ impl<'ccx, 'tcx> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
342314
assert_eq!(space, TypeSpace);
343315
let span = ast_generics.lifetimes[index].lifetime.span;
344316
let name = ast_generics.lifetimes[index].lifetime.name;
345-
self.report_bivariance(span, name, suggested_marker_id);
317+
self.report_bivariance(span, name);
346318
}
347319
}
348320

@@ -377,14 +349,14 @@ impl<'ccx, 'tcx> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
377349

378350
fn report_bivariance(&self,
379351
span: Span,
380-
param_name: ast::Name,
381-
suggested_marker_id: Option<ast::DefId>)
352+
param_name: ast::Name)
382353
{
383354
self.tcx().sess.span_err(
384355
span,
385356
&format!("parameter `{}` is never used",
386357
param_name.user_string(self.tcx())));
387358

359+
let suggested_marker_id = self.tcx().lang_items.phantom_data();
388360
match suggested_marker_id {
389361
Some(def_id) => {
390362
self.tcx().sess.fileline_help(

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